Papers by Author: Yong Huh

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Authors: Hong Sun Park, Hyung Ick Kim, Yong Huh, Moon Young Kim, Sang Yeol Park, Jae Mean Koo, Chang Sung Seok
Abstract: The Ni-based superalloy Inconel 718 (IN-718) was developed in the 1950s and is currently used for several critical gas turbine components due to its good balance of mechanical properties. Because of its stable mechanical properties at high temperature, the alloy is used for turbine bolts. The mechanical properties of in-service facilities are required to maintain safety operation in power plants. Ultrasonic tests, tensile tests and hardness tests were performed to evaluate the degree of the material degradation of Inconel 718. The mechanical properties decreased as degraded, but the longitudinal velocity of the ultrasonic signal increased. Also, the microstructure of the degraded Inconel 718 was to study the relationship between the result from ultrasonic test and the results from destructive methods.
Authors: Hyung Ick Kim, Yong Huh, Jeong Pyo Kim, Chang Sung Seok
Abstract: The mechanical properties of in-service facilities under harsh environment a decrease as materials of the facilities degrade. This decrease of mechanical properties can affect the safety operation of the facilities. Therefore, the extent of degradation due to prolonged service exposure must be estimated. Nondestructive evaluation method is a good technique for monitoring the change of mechanical properties of in-service facilities. The most widely used nondestructive methods are the ultrasonic method and the indentation test, which is advantageous with respect of applicability to in-service facilities. The modified theoretical Vary's equation, considering nonlinear response due to material degradation, was proposed for obtaining the correlations between ultrasonic parameters and fracture toughness. Experimental results showed that ultrasonic attenuation, velocity, and nonlinear parameters have significant correlation with fracture toughness and yield strength. The nondestructive evaluation system can be used to obtain the yield strength and ultrasonic parameters simultaneously, and this information can be used to predict the fracture toughness. The predicted results produced good correlations with the experimental results, indicating that the nondestructive evaluation system can be effective in evaluating material properties and degradation, and the life time of facilities.
Authors: Yong Huh, Hyung Ick Kim, Chang Sung Seok
Abstract: In this study, we performed the static test of nuclear piping materials by the unloading compliance method and the normalization data reduction technique and obtained two fracture resistance curves (J-R curves). The two curves were similar, which proves that the normalization data reduction technique can be adopted in the static test. Then we performed the dynamic fracture toughness test for welding part of nuclear piping. The J-R curves were obtained from the dynamic test by the normalization data reduction technique and were compared to those of the static test results.
Authors: Hyung Ick Kim, Yong Huh, Jae Sil Park, Chang Sung Seok
Abstract: The safety and reliability of industrial machineries and structures used in various, and severe conditions has become an increasing concern. This study proposes ductile-brittle transition temperature (DBTT) evaluation technique by the sub-sized specimen test to prevent cleavage fracture. Four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared. The fracture toughness tests were performed on sub-sized specimens both at room and low temperatures. The results of the fracture toughness tests were analyzed to obtain the DBT behaviours of the specimen materials
Authors: Yong Huh, Sung Keun Cho, Hyung Ick Kim, Chang Sung Seok
Abstract: In this study, the plastic η -factors of the SA508Cl.1a narrow-gap welding part, which is used for the primary piping system in a nuclear power plant were obtained by using finite element analysis and the modified fracture toughness testing method was suggested for the narrow-gap welding part. Also, we have performed the fracture toughness test for the SA508Cl.1a narrow-gap welding part by applying the new testing method and then we compared the results with those from the ASTM fracture toughness test.
Authors: Chang Sung Seok, Bong Kook Bae, Jae Mean Koo, Jae Sil Park, Yong Huh
Abstract: In the case of inner pressurized pipe, the hoop stress mainly causes the failure of pipe. For evaluating the hoop tensile properties of pipes, a ring test is used although it has an inevitable shortcoming of disturbance by the bending. Arsene suggested a central piece-inserted ring test for reducing the bending. At high temperatures, the friction between the specimen and the central piece exerts a serious influence on the results, so an effect on friction should be considered in the analysis. In this study, for the evaluation of the hoop properties using the central piece-inserted ring model of Arsene, we performed the ring tensile tests at several temperatures. From the ring tensile tests and numerical analysis the load-displacement conversion relationship of ring specimen (LCRR) was determined. We could obtain the hoop tensile properties by means of applying the LCRR to the results of the ring tensile test. From the result, it was observed that the strength decreased as the temperature increased, and the elongation dropped a little around 400°C.
Authors: Young Min Lee, Yong Huh, Jae Sil Park, Chang Sung Seok
Abstract: Generally, the shape of graphite and the contents of elements strongly affect the tensile strength of cast iron. In this study, hardness tests and tensile tests for the two types of gray cast iron were carried out. The test results showed the similarity in the hardness but considerable difference in the tensile strength between two materials. Microstructure analysis and chemical analysis were conducted to determine the cause for the difference in the tensile strength between the two types of cast iron. The experimental results showed differences in the microstructure and chemical composition between the two materials. B-type brake disk material(B-type) that had higher tensile strength includes flake, vermicular and spheroidal graphite, whereas A-type brake disk material (A-type) included only flake graphite in the structure. Nodularity of graphite in the B-type was higher than that in the A-type. Also, the B-type had the higher Si content and lower Mn content. In addition, the B-type had Cu, while the A-type did not. Therefore, we concluded that the difference in the strength between the two types of cast iron was due to the difference in the shape of the graphite and the contents of Cu in the cast irons.
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